This invention relates generally to methods and apparatus for building cylindrical tanks using coils of metal, such as steel, and more particularly to a weld seam opening regulator that aligns and spaces a metal band from a coil with a portion of a cylindrical tank prior to the two being welded together. The methods and apparatus enhance weld quality and uniformity, and are readily adaptable to automatic weld seam opening adjustment.
Coil steel tank building processes are known from various sources such as Oostwouder European Publication No. 282 126, wherein a cylindrical tank is built from coiled sheets of stainless steel. Cylindrical tank portions or rings are made by unwinding a band of steel from a coil, passing it over rollers spaced to the desired tank diameter, cut to length, and welded at its ends to form a cylindrical ring. The ring is then raised up with jacks, aligned with a second band of steel from the coil, and the two are welded together along a horizontal weld seam. This process is repeated until a desired tank height is achieved. Preferably, a welding station for joining the two component parts remains stationary and the ring and band of coil steel are rotated so that the point of merger between the band of coil steel and the ring also remains stationary near the welding station.
Originally, the cylindrical portion of the tank and the band of coil steel were aligned by a system of rollers, such as items 24 and 25 of FIG. 1 in European Publication '126. One pair of rollers was positioned inside the cylindrical structure and one pair of rollers was positioned outside of the band of coil steel. By varying the angle between the pairs of rollers and the spacing of the rollers, the band of coil steel was aligned with the cylindrical tank portion. Vertical forces from supporting rollers were applied to vary the spacing of the steel band and the cylindrical structure. Due to variations in steel surfaces and thicknesses, the forces applied by the rollers vary and result in variations in the vertical and horizontal spacings of the steel band and the cylindrical tank portion. These variations reduce welding efficiency and reliability of a full penetration welded joint between the cylindrical tank portions.
Another example of a cylindrical tank building method is disclosed in U.S. Pat. No. 4,494,291 wherein apparatus for constructing cylindrical storage tanks and a fitting frame 15 are described. A band of steel is supported by support and guide rollers 116 and 117. A push-down roller 132 and a push-out roller 125 aid in alignment. The fitting frame 15 is not stationary and it rotates around the tank on wheels with the coil steel. Further, vertical spacing between the band of steel and the upper cylindrical portion is controlled without the benefit of a lower roller that provides a reaction force and surface from which weld seam spacing can be set. The spacing is set by visual adjustment by an experienced operator and apparently requires constant adjustment as the fitting frame travels around in circles on uneven ground.
Next, U.S. Pat. Nos. 4,121,747; 4,047,847; and 4,142,284 disclose a welded storage tank construction method in which the steel strips are welded into a spiral to form a tank. There is no single device that bears on both the steel band and the already formed upper cylindrical portion to align the two and there is no disclosure of a device that aligns a steel band with an upper cylindrical portion and also sets the vertical weld seam opening dimension.
U.S. Pat. No. 4,618,757 discloses a method for making a cylindrical tank by unwinding a band of steel into alignment with a previously made upper cylindrical portion. Rollers 33 are used to align the band with the upper cylindrical portion, but the rollers have no ability to adjust the vertical weld seam opening dimension.
U.S. Pat. Nos. 3,337,384 and 3,206,899 disclose an apparatus for making walled structures. The device in these patents rotates about an axis to add strips of material onto the structure from the ground up. The apparatus includes lateral guide rollers 90 and 92 and small rollers 102 and 103 to "prevent the previously sealed wall and the feed strip from prematurely contacting the surface of the heater plate 82, thus assuring more uniform heating of the sealing surfaces." (Col. 5, lines 13 to 16.) Although the rollers 102 and 103 do provide some vertical spacing prior to the layers being fused together, they are not capable of maintaining the two layers in a spaced relationship to accept a downstream weld.
Finally, U.S. Pat. No. 3,838,496 discloses a welding machine that rides on top of sheets of steel as they are added to a tank. Numerous stabilizing rollers are used to align parts to be welded.
Thus, there is a need in these cylindrical tank building methods for a simple weld seam opening regulator and regulating method that can align a band of steel with an existing cylindrical tank portion to achieve constant spacing at a welding station for improved welding efficiency and uniformity. Further, it is desirable that such regulator apparatus and methods be automatically adjustable for improved tank building efficiency and convenience.